The molecular structures of muscle and electroplax acetylcholine receptors appear to be complex, consisting of several polypeptides of different molecular weights. Only one of the chains has been assigned a function. The alpha subunit reacts specifically with bromoacetylcholine and MBTA and, therefore, possesses a cholinergic ligand binding site. The functions of the other polypeptides are unknown and their authenticity as parts of the receptor has been questioned. We are applying both biochemical and immunological techniques to the study of the putative subunits in order to elucidate their functions. The reactivity of isolated subunits with 125I-alphaBuTx is being investigated. Also, mono-clonal antibodies to the ACh receptor are being produced for use in functional and anatomical studies.